While the military accomplishments of the Mongols have been well chronicled, mostly by their defeated adversaries, their cultural life lays buried beneath the dry soil and scrub grass of the Central Asian steppe. Only cryptic evidence remains for historians to work with and even that has been warped by centuries of foreign intrusions.

Researchers have to grapple with three problems. First, the Mongols had no written language until Genghis adopted the Uiger script in the thirteenth century. Whereas their neighbors in China and the Muslim lands had been recording their cultural exploits in writing for countless generations, the Mongols passed theirs down by word of mouth. All written literature has its roots in an oral tradition— Homer's epics, for example, were recited by traveling storytellers for thousands of years before they were copied down. But that event happened relatively early in...